The present invention is generally directed to motion picture projectors and more particularly to a forward-reverse and multiple speed film transport mechanism for motion picture projectors.
Film transport mechanisms for use in motion picture projectors are well known in the art. Conventional mechanisms of this type may comprise a shuttle arranged for "up-and-down" or vertical reciprocation. The shuttle is also arranged for "in-and-out" reciprocation so that a tooth or teeth carried thereby disengage the film perforations at the end of each advancing stroke and engage the perforations just prior to and during an indexing stroke. The shuttle is driven for vertical reciprocating motion by a transport cam against which the shuttle is disposed.
Such mechanisms additionally include a rotary shutter having a plurality of radially extending shutter blades, a given one of which covers the projector aperture during both forward and reverse projection. With many mechanisms of the prior art, in order to switch between forward and reverse film transportation, it has been necessary to reverse the direction of angular rotation of a shaft which is coupled to the transport cam and shutter to provide for properly synchronized forward and reverse film transportation. In other words, the direction of rotation of the rotating shaft is reversed so that the shuttle is caused to engage with the film perforations during its downward stroke for forward projection as opposed to engaging the film during its reverse stroke for reverse projection. When reversing the direction of film transportation in this manner, the same shutter blade covers the projection aperture as the film is transported. However, these arrangements are complicated and expensive in that they require complex cam arrangements.
To overcome these deficiencies, film transportation mechanisms have been devised wherein the phase relationship between the in-out and up-down cams are changed to allow for switching between forward and reverse film transportation without requiring reversal of the direction of rotation of the rotating shaft. While mechanisms of this variety have proven useful, they have experienced some difficulties. Such mechanisms require either temporary disengagement between various components when the direction of film transportation is changed to thereby exert high torque forces on such components or require cam arrangements which are shifted relative to one another. Because the timing between the in-out, up-down cams and shutter blades is critical, such arrangements are difficult to manufacture because of the required manufacturing tolerances and precise manual alignment of the various components.
It is therefore a general object of the present invention to provide a new and improved film transport mechanism for a motion picture projector.
It is another object of the present invention to provide an improved film transport mechanism for a motion picture projector which allows the direction of film feed to be reversed without requiring a reversal of the direction of rotation of the driven rotating shaft.
It is a still further object of the present invention to provide a forward-reverse film transport mechanism which is easier to assemble and maintain in operation.
It is a still more particular object of the present invention to provide a forward-reverse film transport mechanism which is less complicated than those of the prior art and which includes fewer component parts.